1. Field of the Invention
The present invention relates generally to systems for capturing and recovering vapors emitted from containers, and more specifically to a vapor recovery system for large, stationary hydrocarbon storage tanks, as used in the petroleum industry. The system provides for the cooling and condensing of the vapors by using water spray into the vapor recovery area, as well as a coolant jacket around the vapor recovery area.
2. Description of the Related Art
Increasing environmental awareness has led to the realization that many industrial products and processes may be potentially harmful to humans as well as to the environment. The recognition of the potential harmful effects of such processes and products has led to the establishment of the federal Environmental Protection Agency, as well as other federal and state agencies, in order to regulate and control such products and processes.
Perhaps the most prevalent example of the need for such control is in the petroleum industry, where it has been established that many petroleum products are not only toxic, but are also carcinogens. This is especially true of many of the lighter fractions of petroleum products, formed of relatively light weight molecules and having relatively high vapor pressures. In the past, such products were routinely vented to the atmosphere, in order to prevent the excessive buildup of pressure within the storage tanks, and possible rupture of the tanks and resulting fuel spills. The need to alleviate the pressure buildup within petroleum storage tanks still exists, however, even though the uncontrolled venting of hydrocarbon vapors into the atmosphere is generally prohibited now. Moreover, the release of hydrocarbon vapors and VOC (volatile organic compounds) into the atmosphere is quite wasteful of these finite resources, and recovery of these vapors has become increasingly important economically, as well as ecologically.
Accordingly, a need has been established for some means to capture and recover vapors from hydrocarbon and VOC storage tanks and the like. While various devices and systems have been developed in the past, they differ in various respects from the present invention. A discussion of the related art of which the present inventor is aware, and its differences and distinctions from the present invention, is presented immediately below.
U.S. Pat. No. 1,051,051 issued on Jan. 21, 1913 to Alois Zeckendorf describes a Process Of Regaining Alcohol From Air Passed Through Fermenting Vats Or The Like. Zeckendorf uses steam vapor to absorb the vaporous alcohol, with the steam and alcohol being cooled and condensed back to liquid form in a following step. However, Zeckendorf makes no provision for separating the condensed mixture into its water and alcohol components, stating that "the alcohol is not excessively diluted by water" (column 1, lines 46-47), yet it is well known that alcohol and water mix readily together and do not readily separate. Zeckendorf further teaches away from the present invention, by heating the water to form steam before spraying it into the alcohol vapors. The use of heated steam in the present invention, would raise the temperature at that point even higher, thus further increasing the vapor pressure of the VOCs and making them even more difficult to recover. The present invention uses water which has been chilled or is at least no higher than ambient temperature, to cool the vapors and reduce their vapor pressure for condensation back to liquid form. Moreover, the use of such a water (or other immiscible liquid) to cool the VOC vapors results in a liquid state for both substances, where the water and liquid hydrocarbons do not readily mix, but rather separate naturally for ease of further processing.
U.S. Pat. No. 2,758,665 issued on Aug. 14, 1956 to Alex W. Francis, Jr. describes Low Temperature Separation Systems for separating liquid hydrocarbon vapors from gases at the well stream. The "low temperature" used is from 60 to 90 degrees (column 4, line 74), in order to drive as much gas as possible from the liquid hydrocarbon fraction. This is considerably higher than temperatures used in the present invention. Moreover, since Francis, Jr. is separating substances directly from the well head, with its relatively high pressures, he cannot vent any of the system to ambient, as is done with the present system. Francis, Jr. also uses a desiccant (glycol, etc.) in his system, which is not required for recovery of hydrocarbon vapors using the present system.
U.S. Pat. No. 3,791,422 issued on Feb. 12, 1974 to Everette M. Johnson et al. describes a Service Station Gasoline Vapor Recovery System comprising a concentric vapor recovery line within a conventional fuel delivery hose. Vapors displaced from the automobile fuel tank are recovered and sent to a knockout chamber or cooling tower, where the vapors are condensed back to liquid form and sent back to the stationary storage tank via a one way valve. The system differs from the present invention, in that (1) no water or other coolant is injected into the vapor, (2) the vapor is returned to a different tank from that from which it escaped, and (3) the system is structured to act only intermittently and temporarily, with the fuel hose being removed from the vehicle fuel tank inlet between uses.
U.S. Pat. No. 4,110,091 issued on Aug. 29, 1978 to Werner Daeschler et al. describes a Process For The Separation Of A Gaseous Mixture Consisting Of Water Vapor, Hydrocarbons, And Air. The process is a closed system, with the gaseous mixture being compressed and then chilled a closed network of components, unlike the present system which is open to ambient pressure. Moreover, Daeschler et al. chill the gaseous mixture far below temperatures used in the present system, with the Daeschler et al. system reaching temperatures sufficiently low to cause the hydrocarbon fractions to solidify (column 1, lines 45-47, etc.). While the present system may use cooling agents other than water to cool the mixture below the freezing point of water, it is not considered desirable to cool the mixture below the freezing point of the hydrocarbons therein. Thus, Daeschler et al. teach away from the present system, which preferably uses water as the cooling agent, or at least a cooling agent which does not produce temperatures substantially below the freezing point of water. Moreover, the present system is structured to operate continually, while the Daeschler et al. system operates only intermittently on demand, somewhat like the Johnson et al. service station system discussed further above. Also, Daeschler et al. must provide supplemental heat for their system to remove water ice which has formed, and also provide for air to be passed through the system to assist in the evaporation and removal of ice therein. This is considerably different than the operation of the present vapor recovery system.
U.S. Pat. No. 5,234,552 issued on Aug. 10, 1993 to Robert McGrew et al. describes a Glycol Reboiler Vapor Condensor for recovering the glycol vapors from a moist hydrocarbon recovery system. This patent is generally directed to a system for recovering a mixture of gas and liquid hydrocarbons at the well, rather than recovering hydrocarbon vapors from a storage tank, where the hydrocarbons are essentially dehydrated. Such a system is described in U.S. Pat. No. 2,758,665 to Alex W. Francis, Jr., discussed further above. In such gas and hydrocarbon recovery, it is important to avoid or minimize any hydration of the gas fraction. Yet, in order to condense the liquid hydrocarbons to precipitate from the gas, it is generally necessary to cool the mixture below the water condensation point in the gas. Accordingly, glycol (or other desiccant) is added to the mixture to absorb water. The hydrated glycol must then be dehydrated, with the McGrew '552 patent disclosing a means of accomplishing such glycol dehydration. The cooling water temperature used is generally considerably higher than that used in the present invention, and no additional cooling of the coolant is provided in the '552 patent, whereas additional cooling of the water is a part of the system of the present invention. Also, the '552 patent provides for burning the released hydrocarbons to provide heat for the glycol reboiler, which heating is not a part of the present invention. The temperatures reached in the glycol reboiling operation can be as high as 400 degrees F., whereas no heating means or temperatures above ambient are provided in the system of the present invention.
U.S. Pat. No. 5,255,735 issued on Oct. 26, 1993 to Ram S. Raghava et al. describes a Fuel Vapor Recovery Device for automobile fuel tanks comprising an insulated catch container adapted to cool and condense fuel vapors within the fuel tank, and to return them to the tank in a liquid state. The device amounts to a small refrigeration unit, and is an entirely closed system, excepting the air vent to ambient which is only selectively and periodically opened. Moreover, while Raghava et al. state that the "device would operate continuously" (column 3, lines 45-46), this means only that continuous electrical power would be provided. The device is only intended to collect vapors during the warmer portion of the diurnal cycle and return them to the tank intermittently, as indicated in column 3, lines 24-34. The present system operates continually, and is continuously open to ambient conditions.
U.S. Pat. No. 5,429,667 issued on Jul. 4, 1995 to Karl Ebner et al. describes a Process For The Recovery Of Carbon Disulfide From A Steam/Carbon Disulfide Mixture. The system is closed, unlike the present system which is open to ambient conditions. The initial cooling water spray is preheated in a heat exchanger, which teaches away from the present system where water at ambient or lower temperature is used. It is not desirable to use heated water in the present system, as the addition of heat would tend to promote the formation of additional hydrocarbon vapors.
U.S. Pat. No. 5,431,715 issued on Jul. 11, 1995 to Beth O. Teague et al. describes a Process For Removing Emissions By Condensation And Precipitation, essentially comprising a heat exchanger for cooling the air and contaminate mixture to condense the contaminates into droplets, a liquid removal system, and another heat exchanger for reheating the air. The liquid removal system of the Teague patent relies upon principles such as electrostatic precipitation, filter pads, etc. Teague does not use cooling to separate the contaminates from the air, as is done in the present invention. Moreover, the present invention does not use any heating means anywhere in the system. The use of heat teaches away from the present invention, where heat is undesirable due to its effect in further vaporizing the hydrocarbons which are being condensed from the air. Also, the Teague system appears to be a closed system, unlike the present system which is open to ambient conditions.
Japanese Patent Publication No. 53-90157 published on Aug. 8, 1978 illustrates a system for treatment of waste gas containing another substance(s) therein. The English abstract indicates that the method comprises passing the gas through a heat exchanger, and presumably cooling the gas to condense the substance from the gas, to cause the substance to flow down the inner surface of the condenser. While this method bears some resemblance to that used in the present invention, it is not clear whether the system is closed or open to ambient conditions, as in the present invention, nor is any form of water or other liquid spray apparent for directly cooling the gas, as provided by the present invention.
Finally, German Patent Publication No. 3,827,813 published on Feb. 22, 1990 illustrates a means of condensing petrol (gasoline, i. e. hydrocarbon) vapor from waste gas. The system uses liquid nitrogen to cool an intermediate medium, which is in turn used to chill the waste gas and condense the hydrocarbon vapors therein. An additional step is required first to dry the waste gas or air and vapor mixture completely, as the temperatures of the process are well below the freezing point of water. This relatively complex system teaches away from the present invention, where water is injected into the hydrocarbon vapor to condense the vapor to a liquid state. This is not a problem, as light hydrocarbons (e. g., gasoline) do not mix readily with water and are easily separable in a collection tank.
None of the above inventions and patents, either singly or in combination, is seen to describe the instant invention as claimed.